I've looked at the log files and I can't find a more unique way to describe the two cameras in an Applescript than using their model names. The camera switching works well using Aptivate to assign a key for each script. You can't switch them quickly. But, at a normal working pace it works.

Does anyone know a way to uniquely describe two cameras of the same model?

I may have to cheat and use D800 & D810s or D600 & D610s… Not ideal. But it may work until I get a better solution.